The accusations were made by a watchdog group about a factory in Dongguan in Southern China.

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Three activists investigating labor conditions there have either been arrested or have disappeared.

The company says it stopped making Ivanka Trump brand shoes in March. There is growing concern about the fate of the missing investigators.

Three men working for a U.S.-based organization called China Labor Watch have been documenting poor working conditions in China for 17 years, reports CBS News correspondent Ben Tracy.

Leaders of the organization say they have never seen the Chinese government crack down on them in this way and think the Trump name has something to do with it.

The Ivanka Trump fashion line is all about style and sophistication and it has grown into a $50 million brand.

But this is the other reality -- some of her shoes have been made here at the Huajian International shoe factory in Dongguan, China.

China Labor Watch says three men have been investigating poor working conditions at two of Huajian's factories since last year and claim they documented workdays that often last longer than 18 hours or pay less than China's minimum wage. They also claimed repeated verbal abuse.Now, the organization says all three men have been missing since at least Sunday.The wife of Hua Haifeng told CBS News that the police have detained her husband and accused him of "illegal surveillance." William Hurst is a professor at Northwestern University and a board member of China Labor Watch.

"This is the first time that activists, or investigators, working in any way in collaboration with China Labor Watch have been detained in this manner," Hurst said.

China Labor Watch has spent nearly two decades investigating Chinese manufacturing companies that produce products for U.S. businesses, such as Apple and Disney.

In April, the organization says it sent a letter to Ivanka Trump pointing out their concerns, but received no reply.Marc Fisher Footwear, the company that licenses Ivanka Trump's name, told CBS News, "We were unaware of the allegations and will look into them immediately."Ivanka Trump is well known in China, especially after videos of her daughter singing in Mandarin went viral.Her husband Jared Kushner has been seen as instrumental in arranging the meeting between Chinese President Xi and President Trump in Florida back in April.

China Labor Watch admits they chose the Huajian factory in part because it produced Ivanka Trump shoes and they knew it would bring attention to the labor issues here in China.

CBS News wanted to ask Ivanka Trump's brand if they plan to continue making goods overseas despite President Trump's "America First" policy but they did not respond.